The invention is based on a wiper bearing.
Wiper systems with multiple windshield wipers for motor vehicles are fastened with their wiper bearings directly or indirectly to a body of the motor vehicle, via a mounting plate. The mounting plate has a wiper drive mechanism with a wiper motor, whose motor shaft, via a set of rods, drives cranks that are solidly joined to one end of a drive shaft for each windshield wiper. It is also possible for only the drive shaft of one windshield wiper to be driven by the wiper motor, while another windshield wiper is connected to the first windshield wiper via a four-bar lever mechanism and has a bearing axis. The drive shaft or bearing axis is supported in a wiper bearing. The remarks hereinafter will be made with regard to a drive shaft for a bearing axis that will no longer be mentioned expressly.
At least one radial bearing is provided in the bearing housing, and on the face ends between the bearing housing and a part solidly joined to the drive shaft, an axial bearing is provided. The drive shaft protrudes out of the vehicle body and moves a wiper arm, secured to its free end, with a wiper blade over a windshield. The wiper arm has a fastening part, connected to the drive shaft, that is pivotably connected to a hinge part that is rigidly adjoined by a wiper rod. The wiper blade is suspended in a bracketlike end of the wiper rod.
As a rule, the wiper bearings have a bearing housing of zinc or plastic. In a zinc bearing housing, bearing bushes are press-fitted into fits or bush seats, and the bearing bushes radial guide the drive shaft. In a plastic bearing housing, the drive shaft can be radially supported directly in a fit or in a bearing bush press-fitted into a bush seat. In the case of zinc and plastic, the fits and bush seats can be made by die casting and injection molding, respectively. The bush seats require only little postmachining, if any.
To save weight compared with a zinc bearing housing and gain greater rigidity compared to a plastic bearing housing and higher dimensional stability, or to avoid material flow, it is known to make bearing housings out of aluminum or an aluminum alloy. In an aluminum bearing housing, as in a zinc bearing housing, bearing bushes are press-fitted into fits or bush seats. Aluminum has the property of shrinking onto a casting tool upon curing, so that especially in the case of relatively long fits or bush seats, these elements have to be postmachined. There is also increased wear on the casting tool.
According to the invention, a bush seat of a bearing housing has at least two conical jacket faces, tapering in the mounting direction, which are preferably separated from one another by at least one radially inward-extending shoulder. With one or preferably more shoulders, despite steep, short jacket faces, a great change in diameter in the mounting direction of the bearing bush can be attained. As a result of the great change in diameter, a short joining distance of the bearing bush upon installation and a short unmolding distance of the bearing housing out of a casting tool are attained. When the bearing housing is removed from the casting tool, at first even after a short axial unmolding distance, faces of the casting tool are far away from the jacket faces of the bush seat. The unmolding is facilitated, and in particular wear of the casting tools and the requisite postmachining of the bush seat are reduced or largely avoided.
In the mounting or assembly process, first a small outer diameter of the bearing bush meets a large inside diameter of the bush seat, and only shortly before the bearing bush is fully introduced into the bush seat do jacket faces of the bearing bush come to rest, over a short joining distance, on the jacket faces of the bush seat. Installation is facilitated, and incorrect installation where the bearing bush is inserted with the wrong face end first is avoided. The jacket faces of the bush seat can be embodied steeply, with a requisite casting obliquity for unmolding of about 1xc2x0 to 2xc2x0 , despite a great change in diameter.
The drive shaft is driven by cranks and moves a wiper arm with a wiper blade over a windshield. This creates shear forces acting periodically on the drive shaft. The shear forces are supported via the bearing bush, the bearing housing, and the mounting plate on the vehicle body. Because of the conical faces between the bearing bush and the bearing housing, a force component counter to the mounting direction arises. However, with steep jacket faces, this force component is especially small, and the bearing bush remains reliably secured without play in the bearing housing. Also with steep jacket faces and an only slight mounting force, reliable self-locking is attained, and at even a small radially inward-oriented pressure onto the bearing bush, a secure, firm connection is made. The bearing bush largely retains its shape and especially its inside diameter, so that a drive shaft can easily be introduced into the bearing bush and guided exactly by it without play, without requiring major calibration effort or expense.
The bearing housing according to the invention of a wiper bearing having the stepped bush seat can be cast from zinc, plastic, or some other material thought suitable by one skilled in the art. Especially advantageously, however, the invention is employed with materials that are difficult to unmold, as in the case of bearing housings of aluminum or an aluminum alloy. Aluminum bearing housings are especially lightweight and rigid and can easily be unmolded with little wear from a casting tool, because of the short jacket faces and great change in diameter of the bush seat that are provided according to the invention. Postmachining of the bush seat is furthermore avoided largely or even completely.
In one feature of the invention, the bearing bush has a collar. The drive shaft can be supported on the collar of the bearing bush on an advantageous, large axial bearing face. Furthermore, the collar can be used as a radial running face for a lip seal.
Production variations of the bearing housing can change the length of the bearing housing and the axial positions of the shoulders. To achieve an exact spacing between two axial bearing faces or an exact length of the bearing housing with one or two bearing bushes, the bearing bushes are press-fitted to size and with their face ends form axial bearing faces, in particular bearing bushes with a collar. In order for the bearing bush to be securely fixed in the mounting direction, it advantageously rests on a stop.
According to the invention, at least one and preferably all the shoulders are disposed offset counter to the mounting direction, so that when the bearing bush is press-fitted to size, the bearing bush is plastically deformed at the shoulders. The length of the bearing housing having the bearing bush can be brought to exact size, and the bearing bush rests on a stop. It is also assured that the bearing bush is fastened with a secure hold, without play, in the bearing housing. In the region of the shoulder, as a result of the plastic deformation, material comprising the bearing bush places itself without play over the circumference on the bush seat.
The plastic deformation can cause material of the bearing bush to be cast off inward. In one feature, it is provided that in the mounting of the bearing bush, a cylindrical pin is disposed in the bearing bush. As a result, the bearing bush can be calibrated in a single step axially and, by the cylindrical pin, radially.